PCSK1 and type 2 diabetes mellitus: Proinsulin processing is impaired in patients with type 2 diabetes (T2D), but messenger RNA expression of the evolutionary conserved enzyme proprotein convertase subtilisin/kexin type 1 (Pcsk1) (refs. 9,10) and other proinsulin processing enzymes appears to be unaffected in pancreatic islets from T2D donors11, indicating that post-transcriptional pathomechanisms may impact insulin processing.